Plastic knobs have long been used as manually engageable elements threaded on the ends of control shafts or levers. Such knobs have conventionally been of solid construction. One common prior art construction has comprised styrene, a relatively cheap plastic material, molded about a metal bushing. Butyrate is molded on the outside of the styrene as it has a good appearance while in the past having been of reasonable price. The thin section of butyrate has made molding rather difficult.
Plastic materials used in the manufacture of such knobs have skyrocketed in price in recent years along with the price of petroleum, which comprises the usual basic raw material. By way of specific example, one plastic material widely used sold for something on the order of 15 cents per pound only a few years ago, while the same material now sells on the order of 50 to 60 cents per pound.